The present invention relates generally to novel immunological materials and methods, and more particularly to treatment of horses to confer immunity to infection by Equid Herpesvirus Type 1.
Equine rhinopneumonitis is an infectious disease of horses caused by a viral strain known as Equid Herpesvirus Type 1 (hereafter, "EHV 1"). The disease state is variously characterized by upper respiratory infection, by abortion in pregnant mares, and by neuro-musclar symptoms such as ataxia and paresis. While EHV 1 is known to produce abortion in hamsters, calves are reported to be refractory to infection with this virus.
Commercial vaccines comprising hamster-adapted and tissue cultured live EHV 1 virus have been generally inadequate in controlling the spread of the disease. More particularly, administration of prior art vaccines has frequently been accompanied by incidences of abortion in mares vaccinated during pregnancy and by infection of contact animals by vaccine virus shed nasally after vaccination. As a result, vaccination of pregnant mares is avoided as is vaccination of horses expected to come in contact with unvaccinated mares. There therefore exists a need for vaccine materials and methods which confer immunity to infection by EHV 1 but which are safe when administered to pregnant mares and which do not give rise to shedding of infective vaccine virus after vaccination.
This invention has its background in part in the inventor's discovery and isolation of a herpesvirus from the lung of an aborted Hereford fetus. The isolation of this herpesvirus is one of two known isolations from the bovine species. The specific virus isolated by the inventor was shown by him to possess physical properties common to those of the herpesviruses, e.g., typical herpesvirus morphology as confirmed by electron microscopic studies. The virus was found to be sensitive to chloroform and its replication was inhibited by 5-iodo-deoxyuridine. Initial serum neutralization tests using diluted typing sera specific for EHV 1 showed the newly-isolated viral strain (designated "Bovine Herpesvirus No. 1247") to be distinct from, inter alia, the equine herpesvirus responsible for equine rhinopneumonitis. See, generally, Crandell, et al, "Theriogenology", 6, pp. 1-19, (1976). Subsequent independent studies of samples of the new virus showed, however, the existence of serologic relation with other viruses, and specifically with EHV 1. See, Kanitz, et al, "Proceedings, 19th Meeting American Association of Veterinary Laboratory Diagnosticians," pp. 1-12 (Nov. 1976) and Smith, "Proceedings, 80th, Meeting, U.S. Animal Health Association," pp. 149-158, (1976).
In a comparative study of Bovine Herpesvirus No. 1247 and EHV 1, the inventor ascertained that the bovine virus was in fact nasally infective in horses, generating a mild rhinitis and increase in rectal temperature. The inoculated ponies developed measurable serum neutralizing antibodies to the vaccine virus as well as to the equine virus (EHV 1).